Electrical insulation system with improved electrical breakdown strength, said electrical insulation system comprising a hardened polymer component having incorporated therein a conventional filler material and a selected nano-scale sized filler material, wherein (a) said hardened polymer component is selected from epoxy resin compositions, polyesters, polyamides, polybutylene terephthalate, polyurethanes and polydicyclopentadiene, and preferably is a hardened epoxy resin system; (b) said conventional filler material is a known filler material having an average grain size distribution within the range of 1 µm-500 µm, being present in a quantity within the range of 40%-65% by weight, calculated to the total weight of the insulator system; and (c) said selected nano-scale sized silica powder is a pretreated nano-scale sized filler material, having been produced by a sol- gel process; wherein said selected nano-scale sized silica powder is present within the electrical insulation system in an amount of about l%-20% by weight, calculated to the weight of the conventional filler material present in the electrical insulator system; method of preparing said insulations; and electrical insulation system containing the components (a) and (c) only.

Electrical insulation system with improved electrical breakdown strength, including a hardened polymer component having incorporated therein a filler material and a nano-scale sized filler material. The hardened polymer component is selected from epoxy resin compositions, polyesters, polyamides, polybutylene terephthalate, polyurethanes and polydicyclo-pentadiene. The filler material has an average particle size within the range of 1 mum-500 mum, and is present in a quantity within the range of 40%-65% by weight, calculated to the total weight of the insulation system. The nano-scale sized filler material is a pretreated nano-scale sized filler material, having been produced by a sol-gel process. The nano-scale sized filler material is present within the electrical insulation system in an amount of about 1%-20% by weight, calculated to the weight of the filler material present in the electrical insulation system.